Radial roller anti-friction transmission with eccentric bushings

ABSTRACT

A mechanical transmission having an anti-friction nut construction which comprises an annular body member provided with a longitudinal bore to receive a cooperable member in the form of a screw or bar, and with a plurality of roller elements extending radially into the bore for engagement with side wall surfaces of the cooperable member. The body has sockets in which there are eccentric bushing assemblages carrying the roller elements on anti-friction bearings. The assemblages are rotatable in the sockets, and thus the positions of the roller elements can be minutely adjustably shifted laterally. Locking means secure the assemblages against movement once they are properly positioned. The above arrangement enables a given nut to be used with screws or bars of slightly differing tolerances and pitches, since the roller elements can be shifted within limits to accommodate the slight inevitable manufacturing variations. Alternately, the bushing assemblages can be adjusted so the rollers engage opposite side walls of the groove of the screw or bar, and thus backlash can be reduced to zero. The assemblages are easily removable from the body to facilitate servicing and replacement.

United States Patent 1 Metz [4 Oct. 23, 1973 RADIAL ROLLER ANTI-FRICTIONPrimary Examiner-Leonard H. Gerin Attorney-H. Gibner Lehmann et al.

[57] ABSTRACT A mechanical transmission having an anti-friction nutconstruction which comprises an annular body member provided with alongitudinal bore to receive a cooperable member in the form of a screwor bar, and with a plurality of roller elements extending radially intothe bore for engagement with side wall surfaces of the cooperablemember. The body has sockets in which there are eccentric bushingassemblages carrying the roller elements on anti-friction bearings. Theassemblages are rotatable in the sockets, and thus the positions of theroller elements can be minutely adjustably shifted laterally. Lockingmeans secure the assemblages against movement once they are properlypositioned. The above arrangement enables a given nut to be used withscrews or bars of slightly differing tolerances and pitches, since theroller elements can be shifted within limits to accommodate the slightinevitable manufacturing variations. Alternately, the bushingassemblages can be adjusted so the rollers engage opposite side walls ofthe groove of the screw or bar, and thus backlash can be reduced tozero. The assemblages are easily'removable from the body to facilitateservicing and replacement.

17 Claims, 14 Drawing Figures RADIAL ROLLER ANTI-FRICTION TRANSMISSIONWITH ECCENTRIC BUSHINGS BACKGROUND This invention relates to mechanicaltransmissions, and more particularly to devices of this type whichemploy threaded or grooved members such as screws or splined bars. Inthe past a number of transmission drive arrangements employing threadedor splined members and cooperable devices have been proposed andconstructed. In cases where there was substantial contact area between athreaded member and a thread engaging device, both portions had to beconstructed to close tolerances to insure that the load distributionover the areas in contact was reasonably uniform to prevent theoccurrence of excessive localized stresses and excessive wear. Slightvariations in the pitch of threads, from one threaded member to another,frequently resulted in poor efficiency and erratic or unsatisfactoryoperation, as when a given thread engaging device was used with severaldifferent threaded members of varying dimensions. In addition, there wasalmost always a certain amount of backlash between the threaded memberor splined bar and the engaging cooperable device at the time that thetwo changed direction with respect to one another. In certain criticalapplications involving precision equipment, even a small amount ofbacklash could not be tolerated.

SUMMARY The above drawbacks and disadvantages of prior transmissiondevices of the type noted are overcome by the present invention whichhas for an object the provision of a novel anti-friction transmissionmechanism involving engagement between rollers on the one hand andprojections of a shouldered part or threaded member, which transmissionis simple in its construction, reliable in operation, and whichvirtually reduces backlash to zero. A related object is the provisionofa highly efficient transmission device as above noted, wherein theassembly thereof is especially simple so that servicing and maintenanceare greatly facilitated. The above objects are accomplished by a noveland unique antifriction nut comprising an annular body or support memberhaving a longitudinal bore to receive either a threaded member, or asplined bar and having a plurality of roller elements extending radiallytherein for engagement with side wall surfaces of the member or bar. Thesupport member has radial sockets some of which are adapted to receive aunitary assemblage comprising an eccentric bushing, an anti-frictionbearing device carried by the bushing, and a roller element carried bythe anti-friction device. The assemblage when inserted into itsrespective socket is adjustably rotatable therein, and thusthe positionof the roller element can be adjustably changed axially of the supportmember orin other directions. Locking means are provided for securingthe assemblage in any given rotative position once the proper setting ofthe associated roller element has been reached. A centralizing ringdisposed in the bore of the support member and engaging the surface ofthe threaded member is also provided to maintain uniform spacing betweenthe latter and the bore walls.

Other features and advantages of the invention will hereinafter appear.

In the drawings, illustrating several embodiments of the invention:

FIG. 1 is a front elevational view of the anti-friction transmission ofthe present invention, illustrating one embodiment thereof.

FIG. 2 is a vertical sectional view of the transmission taken on line2-2 of FIG. I, particularly illustrating one concentric bushingassemblage and two eccentric bushing assemblages as provided by theinvention.

FIG. 3 is a transverse sectional view of the transmission taken on line3-3 of FIG. 1.. 7

FIG. 4 is a sectional view of one of the eccentric bushings per se ofFIG. 2.

FIG. 5 is a sectional view of the concentric bushing assemblage of FIG.2.

FIG. 6 is a fragmentary sectional view of another embodiment of theinvention, particularly illustrating a modified eccentric bushingreceived in the support member of the transmission and furtherillustrating alternate means of retaining the bushing in the latter.

FIG. 7 is a view like that of FIG. 6 but illustrating yet anotherembodiment of the invention comprising a modified eccentric bushing andmeans for retaining the same.

FIG. 8 is a view like that of FIGS. 6 and 7, illustrating still anotherembodiment of the invention.

FIG. 9 is a sectional view of yet another embodiment of the inventionillustrating a nut having a single roller element carried directly in aradially extending socket thereof, and'also adjustable roller elementsmounted on eccentric bushings disposed in other sockets of the nut body,and further illustrating a cooperable threaded member connected with andadapted to actuate a valve stem. 7

FIG. 10 is a transverse sectional view taken on line l0l0 of FIG. 9.

FIG. 11 is a transverse sectional view of still another embodiment ofthe invention, illustrating a nut having four roller elements mounted oneccentric bushings carried in sockets of the nut body.

FIG. 12 is a frontelevational view of yet another embodiment of theinvention showing a slide hearing or guide such as a splined bar havingtwo longitudinally extending grooves.

FIG. 13 is a section taken on line 13-43 of FIG. 12.

FIG. 14 is a sectional view of a slide bearing similar to that of FIG.12, involving a splined bar having three longitudinally extendinggrooves.

Referring first to FIGS. 1-3 there is illustrated an anti-frictiontransmission part generally designated by the numeral 10, cooperablewith projections or threads 12 of a shouldered part such as a screw 14.The transmission part 10 comprises an annular support member 16 having abore 18 extending alongthe projections or threads of the screw 14 andspaced thereform. As shown in FIGS. 2 and 3, the support member 16 has aplurality of radially disposed sockets 20, 22, 24, 26 and 28communicating with the bore 18 thereof, each being adapted to receive abushing assemblage 30 or 32, illustrated respectively in FIGS. 4 and 5.The sockets 20-28 preferably all have substantially the sameconfiguration and size to enable a given bushing assemblage to bereceived in any particular socket.

In accordance withthe present invention the bushing assemblage 30 is ofconstruction, as illustrated in detail in FIG. 4, wherein the bore 34 ofthe assemblage is eccentric with respect to the outer periphery 36thereof. The assemblage comprises an annular shoulder 37 disposed on theouter periphery 36, and carries a roller element 38 in anti-frictionbearings 40, 42 and 44. The bore 34 of the assemblage is furtherprovided with a threaded portion 46 which receives a threaded cap 48having a slot or key 50 that can be engaged by a suitable tool such as ascrewdriver. Back-to-back spring washers 52 and 54 provide a biasingforce against the roller element 38 through the bearing 44 to therebyurge the roller to a normally advanced position with respect to thebushing body. The bearings 40, 42 and 44 can be press fitted onto theroller element to maintain proper positioning therebetween. Before theassembly of the cap 48 to the assemblage 30, a locking or adhesivecompound is preferably applied to the cap threads so as to preventloosening of the cap after the compound has solidified. This enablesinitial rotational adjustment of the bushing assemblage to be made afterit has been inserted into one of the support member sockets, simply byengaging the slot 50 with a suitable tool as will be explained in moredetail below. It can be readily seen that the axis of rotation of theroller element 38 is non-coincidental with the axis of rotation of thebushing assemblage 30 in its respective socket. Thus, rotation of theassemblage 30 will give rise to a lateral displacement of the axis ofrotation of the roller element 38.

FIG. illustrates a different or concentric bushing assemblage 32 havinga central bore 58 which is concentric with the outer periphery 60. Theassemblage carries a roller element 38 in anti-friction bearings 40, 42and 44. The roller element 38 is secured in place by a threaded cap 48having a slot 50. The cap 48, when tightened, presses against springwashers 52, 54 which in turn provide a biasing force to the rollerelement 38 thereby biasing the latter to a normal, advanced positionwith respect to the bushing body. An annular shoulder 62 is provided tofacilitate mounting of the bushings on the support member 16, as will beexplained below.

FIGS. 2 and 3 illustrate the details of the mounting of the bushingassemblages 30 and 32. The socket 22 has an annular shoulder 64 which isadapted to abut the annular shoulder 62 of the concentric bushing 32,the bushing being inserted radially inward into the socket to the pointwhere the shoulders abut one another. The socket 22 is also providedwith an annular recess 66. With the bushing 32 in place, a splitretainer washer 68 can be installed in the recess to thereby retain thebushing in the socket. In a similar manner, the eccentric bushingassemblages 30 are held captive by means of retainer washers 70 whichare inserted into recesses 76, 78, 79 and 80 of the sockets 20, 24, 26and 28 respectively. The annular shoulders 37 of the bushings 30 abutthe annular shoulders 82, 84, 86 and 88 respectively of the sockets 20,24, 26 and 28, as illustrated in FIGS. 2 and 3.

Referring to FIG. 3, in accordance with the present invention, thesupport member 16 is further provided with a tapped bore 90communicating with the socket 22, and means carried by the member 16 forlocking the bushing 32 against rotation, the means comprising a setscrew 92 adapted to engage the exterior surface of the bushing 32. In asimilar manner, the bushing assemblages 30 can be locked againstrotation by set screws 94, 96 and 98 carried in tapped bores 100, 102and 104 respectively, communicating with sockets 24, 26 and 28respectively.

By the present invention there is further provided an I annularcentralizing ring 105 disposed within the bore 18 of the support member16. The ring centralizes the screw 14 within the bore and insuresuniform engagement of the threads of the screw with the roller elements38, thus minimizing any tendency toward excessive wear of one rollerelement due to nonconcentricity of the screw and support member.

The operation and advantages of the present invention may now be readilyseen. As best illustrated in FIG. 2, the position of the roller element38 of the concentric bushing 32 is axially fixed and not adjustable. Theroller is shown engaging the threads 12 of the screw 14. By the presentinvention, the positions of the pins 38 carried in the eccentricbushings 30 disposed in the sockets 20 and 26 in FIG. 2 (and in thesockets 24, 26 and 28 in FIG. 3) are movable along an axis parallel tothat of the screw, thus enabling compensation for slight variationswhich occur in the thread pitch from one screw to another. Theadjustment of the eccentric bushings can be easily effected. In FIG. 2,the screw can be inserted into the bore 18, such that the roller element38 of the concentric roller assemblage 32, will engage one wall of thethread groove (depending upon the direction of the load applied to thescrew 14). With the eccentric bushings 30 fully inserted in theirrespective sockets 20 and 26, the screw can be advanced further, and theeccentric bushings 30 rotated in their respective sockets in order thatthe roller element of each will just engage the same wall of the threadgroove. The rotation is easily accomplished by engagement with asuitable tool of the slot 50 of each bushing assemblage. After theproper rotary position of each of the eccentric bushings is achieved,they can be locked into position by means of the corresponding setscrews. By the above arrangement, the positions of roller elements canbe easily changed to provide improved load distribution and better loadsharing between the various roller elements. Slight variations in threadpitch from one screw to another can be easily accommodated by the simpleadjustment procedure described above.

It is to be noted that different eccentric bushing assemblages can beemployed in the nut simply by loosening the particular set screw,removing the retainer washer and withdrawing the particular bushingassemblage. This operation can be achieved with a minimum of time andeffort, thus making replacement of the assemblages extremely easy.

Also, it should be noted that it is desirable to keep the eccentricityof the bushings as small as possible while still maintaining an adequaterange for adjustment to enable compensation for the worst case of largescrew thread tolerance. By employing a relatively small eccentricity,the likelihood of the eccentric bushing assemblages being inadvertentlyrotated in their respective sockets by the application of a heavy loadapplied to the screw is minimized. Such an inadvertent rotation wouldupset the adjustment of the rollers carried in the eccentric bushingsand would have an adverse effect upon the operation of the transmission.

Another embodiment of the invention is illustrated in FIG. 6, wherein aneccentric bushing 106 is shown disposed in a radial socket 108 of theannular portion of a support member or nut 110. The bushing 106 has anannular shoulder 112 which is adapted to abut the corresponding shoulder114 of the socket 108. In accordance with the present invention thesocket 108 has an internally threaded portion 116. There is furtherprovided a hollow screw 118 receivable in the socket, the screw havingkeying means or slots 120, 122 engageable by a suitable tool foreffecting rotation thereof. An access opening 126 of the screw isprovided to enable rotary adjustment of the bushing 106. This isaccomplished by loosening the screw 118 and engaging the slot of the cap48 (through the access hole 126) with a suitable tool. Following thisadjustment, the screw 118 can be tightened such that the bushingshoulder 112 is tightly clamped between the socket shoulder 114 and theend portion of the screw 118. A centralizing ring 128, disposed at theend portion of the support member 110, functions in a manner similar tothe ring in FIG. 2, to centralize the screw 14 with respect to theroller elements 38 carried by the support member.

Yet another embodiment of the invention is illustrated in FIG. 7,showing an eccentric bushing 130 having an inturned end 132 whichretains the roller element 134 and bearings 136 and 138. The bushing,roller element and bearings constitute a unitary assemblage insertablein the socket 129 as a single cartridge. The roller element 134 isprovided with a sleeve 135 which is press-fitted thereon. The sleeve 135engages the upper portion of the bearing 136 and thus retains the rollerelement 134 in the bushing 130. An annular bushing 137 is disposedbetween the bearings 136 and 138 to maintain proper spacingtherebetween. The eccentric bushing 130 is provided with a shoulder 139which abuts against a corresponding shoulder 140 of the socket.Shoulders 139 and 140 thus constitute positioning means for theassemblage to limit the insertion thereof to a predetermined amount. Thebushing 130 is secured by means of a spring washer 141 and a retainerwasher 142 which is receivable in a recessed portion 144 of the socket.The spring washer engages the opposite side of the bushing shoulder 139,and thus maintains the latter in engagement with the shoulder 140 of thesocket 129. The rotary adjustment of this assemblage can be effected byengagement of a suitable tool with the slot 50 of the bushing cap 48 asabove described.

Yet another embodiment of the invention is illustrated in FIG. 8,wherein an eccentric bushing 146 is received in the socket 148 frominside the bore of the support member 150. .Under these circumstancesthe socket 148 can have a substantially smooth cylindricalconfiguration. An annular shoulder 152 of the bushing closely abutstheshoulder portion 154 of the socket, thus preventing movement of thebushing in a radially outward direction. Following" the rotaryadjustment of the bushing, the latter can be secured by a set screwarrangement similar-to that shown in FIG. 3. The arrangement of theroller element and bearings of the bushing 146 aresubstantiallyidentical to those of the bushing 130 of FIG. 7. Also, the centralizingring 156 functions in the same manner as the ring 105 of FIGS. 2 and 7.i

A typical application for the transmission of the present invention isillustrated in FIGS. 9 and 10 wherein a nut or shouldered part generallydesignated 160 is provided with a rollerelement 612 which is fixed inits axial position with respect to the nut. The roller element 162 iscarried in anthfriction bearings 164, 166 and 168, the latter beingdisposed in a radially extending socket 170 of the nut. A pair ofback-to-back spring washers 172 and 174 bias the roller element to anormal advanced position with respect to the socket. A threaded cap 17retains the roller and bearings in the bore. In addition to the rollerelement 162 the nut has three eccentric bushing assemblages 106 of thekind illustrated in FIG. 6, the assemblages being disposed in radiallyextending sockets 178, and 182 respectively as illustrated in FIG. 10.The assemblages are retained by means of hollow screws 118 particularlyillustrated in FIG. 6, the screws clamping against the respectiveshoulders 112 thereof.

FIG. 9 illustrates a portion of a screw thread 184 in engagement withthe rollers 38 and 162. The screw carries a valve stem 186 having ports188. The valve stem is received in a valve housing 190 having exit andentry ports 192 and 194, respectively. The nut 160 is connected with ashaft 196 powered by a servo or control motor (not shown) which providespower to rotate the nut for fractional portions of a revolution. Theshaft is secured to the nut by means of bolts extending through themounting holes 191, 193, and 197 of the nut (FIG. 10). In the case wherethe ports 188 of the valve stem 186 are spaced very close to oneanother, it can readily be seen that the positioning of the valve stemin the valve housing can become rather critical, since a small axialdisplacement of the valve stem will give rise to a substantial change insize of the openings for flow. In such a case it is desirable to havenearly zero backlash between the screw 184 (and valve stem 186) and thenut 160.This is readily accomplished by the present invention.

It will be seen that for a given rotary position of the nut 160, theroller element 162 can engage one wall of the groove of the screw 184.Since the oppositely disposed roller 38 (180 from roller 162) is mountedon a bushing assemblage'which is eccentric and adjustable, the lattercan be rotated (by engagement by a suitable tool with the slot 50 in thecap 48) such that the roller element 38 will engage the opposite wall ofthe groove of the screw 184. This arrangement provides virtually zerobacklash since each roller engages an oppositely facing wall of thegroove of the thread. Similarly in FIG. 10, the two rollers 38which aredisposed 90 from the roller 162 can be adjusted so that one will engageone wall of the groove and the other will engage the other wall. As analternative, fora more I balanced arrangement as illustrated in FIG. 9,one pair of diametrically disposed pins can be set to engage one wall ofthe groove, and the other pair setto engage the opposite wall of thegroove. This arrangement has the advantage of not only increasedcompatability with screws of slightly varying pitches, but also providesa means for reducing backlash to negligible proportions.

A slightly modified nut 160a is illustrated in FIG. 11, wherein thenon-eccentric mounted roller 162 of FIGS. 9 and 10 has been replaced bya roller 38 and eccentric bushing assemblage 106 identical to theassemblage i1- lustrated in FIG. 6. By this arrangement the'nut carriesfour eccentric bushing assemblages disposed 90 apart from one another.The adjustment of the assemblages is the same as for the embodimentillustrated in FIGS. 9-10. During adjustment, one of the eccentricassemblages can be set to a mid range or central position, and then theremaining three adjusted for zero backlash as described above.

Other arrangements can be readily devised, subject to the requirementthat all roller elements in excess of one must be carried by eccentricbushing assemblages to enable individual adjustment of the second,third, etc., with respect to the non-adjustable roller element.

Another embodiment of the invention is illustrated in FIGS. 12 and 13,illustrating a slide bearing or longitudinal guide 198 for a splinedshaft 200. The guide comprises an annular body 202 having radiallyextending sockets 204, 206, 208 and 210, 212. Received in the sockets204, 206 and 210 are bushing assemblages 214, identical to thatillustrated in FIG. 6 except the assemblages are concentric rather thaneccentric. Similarly the sockets 208 and 212 house eccentric bushingassemblages 106 identical to that illustrated in FIG. 6. The assemblagesare retained by hollow screws 118 which clamp against the externalannular shoulder of the assemblage in the manner illustrated in FIG. 6.By the above arrangement, wherein the side walls of each of thelongitudinal grooves of the splined shaft are engaged by two rollersmounted on concentric assemblages and one roller mounted on an eccentricassemblage, virtually all play can be eliminated from the bearing.Adjustment is effected by loosening the hollow screw 1 16 and engagingthe cap 48 of the respective eccentric bushing assemblage 106 with asuitable tool and rotating the same in its socket, thus effecting acircumferential shift in the position of the roller elements carriedby'the eccentric bushings. As a result, minute variations in thedimensions of the splined shaft can readily be compensated for with aminimum of effort and with no additional machining.

FIG. 14 illustrates a modified slide bearing 220 for a splined shaft 222having three grooves, the walls of each groove being engaged by tworollers respectively mounted in concentric bushing assemblages 214 andone roller mounted on an eccentric assemblage 106. The adjustment of thethree eccentric bushing assemblages can be readily made in the mannermentioned above to virtually eliminate slop or play between the splinedshaft andthe bearing.

From the above it can be seen that I have provided a novel and improvedanti-friction transmission which is simple in construction, and iseasily serviced and maintained, yet which permits a high degree offlexibility to be obtained. The invention has the advantage ofcompensating for variations in the thread pitch of different screws, andalso has the additional feature of enabling backlash to be reducedvirtually to zero. The adjustment is simple and foolproof. The mechanismof the present invention thus represents a distinct advance andimprovement in the mechanical transmission art.

Variations and modifications are possible without departing from thespirit of the invention.

I claim:

L'An anti-friction transmission mechanism engageable and cooperable withprojections of a shouldered part, comprising in combination:

a. a support member having an annular portion adapted to extend alongthe projections of said shouldered part in spaced relation thereto,

b. a' roller element projecting from the annular portion of the supportmember and arranged for en gagement with side surfaces of theprojections of said part,

c. an additional roller element spaced from the first 6 and projectingfrom the annular portion of the support member and arranged forengagement with side surfaces of the projections of said part,

d. anti-friction bearing devices carrying said roller elements insubstantiallyradial disposition with respect to said annular portion,and

e. means for adjustably mounting said additional roller element on saidmember to enable adjustable positioning of the element axially of saidmember whereby the position of the additional roller element can beadjustably shifted with respect to said first roller element to enableprecise and simultaneous engagement of both roller elements with therespective side surfaces of said shouldered part so as to enable saidmember to be used with shouldered parts made to non-critical tolerances.

2. The invention as in claim 1, wherein:

a. said support member has means defining a socket radially disposedtherein, and

b. said adjustable means comprising an eccentric bushing, the bore ofwhich is eccentric with respect to the outer periphery, said bushingbeing receivable in said socket and turnable therein,

0. said bushing carrying one of said anti-friction bearing devices andsaid additional roller element.

3. The invention as in claim 2, and further including:

a. means carried by said support member, for locking said bushing indifferent adjusted positions in said socket.

4. The invention as in claim 3, wherein:

a. said annular portion has a tapped bore communicating with saidsocket, and

b. said locking means comprises a set screw carried in said bore andengageable with the exterior surface of said bushing.

5. The invention as in claim 3, wherein:

a. said bushing has an external annular shoulder,

b. said socket having a corresponding annular shoulder adapted to abutagainst one surface of said bushing shoulder,

c. said socket further having an annular recess adjacent to itsshoulder,

d. a spring washer adapted to abut against another surface of saidbushing shoulder, and

e. a split ring received in said recess and engaging the spring washerto thereby bias the bushing shoulder into engagementwith the socketshoulder and thus retain the bushing against removal from the socket.

6. The invention as in claim 3, wherein:

a. said bushing has an external annular shoulder,

b. said socket having a corresponding annular shoulder adapted to abutagainst one surface of said bushing shoulder,

c. said annular portion of the support member having a tapped borecommunicating with said socket, and

d. said locking means comprising a set screw carried in said bore andengageable with the lateral surface of said bushing.

7. The invention as in claim 3, wherein:

a. said bushing has keying means engageable by a tool for effectingrotation thereof, to facilitate adjustment of the position of said oneroller element.

8. The invention as in claim 2, wherein:

a. said support member has means defining a second socket radiallydisposed therein,

b. said mounting means comprising an additional bushing adapted to bereceived in said second socket,

c. said bushing carrying the other of said anti-friction bearing devicesand the first-mentioned roller element,

d. said additional bushing and said first-mentioned roller element beingconcentric with one another.

9. The invention as in claim 3, wherein:

a. said bushing has an external annular shoulder,

b. said socket having a corresponding annular shoulder adapted to abutagainst one surface of said bushing shoulder c. said socket having aninternally threaded portion,

d. a screw having a hollow portion for receiving said eccentric bushingand having an annular end portion,

c. said screw being receivable in said threaded portion, and

f. the annular end portion of the screw engaging the annular shoulder ofthe bushing, whereby the latter can be clamped between the socketshoulder and the end portion of the screw when the screw is tightened.

10. The invention as in claim 9, wherein:

a. said bushing has keying means engageable by a tool for turning it,and

b. said screw having an access opening communicating with said hollowcup portion, so as to admit a tool to engage the keying means toadjustably turn the bushing.

11. The invention as in claim 3, wherein:

a. said support member has a longitudinal bore to receive saidshouldered part,

b. said bushing having an external annular shoulder,

c. said socket having a corresponding annular shoulder adapted to abutagainst said bushing shoulder,

d. said bushing being insertable in said socket from said longitudinalbore, and

e. an annular centralizing ring disposed within said bore forcentralizing said shouldered part therein.

12. The invention as in claim 1, wherein:

a. said support member has annular end portions, and b. a centralizingring disposed at an end portion for centralizing the shouldered part insaid member.

13. The invention as in claim 2, wherein:

a. said bushing has an inturned inner end to retain said one bearingdevice and :said additional roller element.

14. The invention as in claim 2, wherein:

a. said bushing carrying one of said anti-friction bearing devices andsaid additional roller element constituting a unitary assemblageinsertable in said socket as a unit,

b. positioning means to limit the insertion of said assemblage to apredetermined amount, and c. retainer means to hold captive theassemblage. 15. The invention as in claim 14, and further including:

a. means carried by said member for locking said assemblage in differentadjusted positions. 16. The invention as set forth in claim 1, andfurther including:

member on the shaft.

1. An anti-friction transmission mechanism engageable and cooperablewith projections of a shouldered part, comprising in combination: a. asupport member having an annular portion adapted to extend along theprojections of said shouldered part in spaced relation thereto, b. aroller element projecting from the annular portion of the support memberand arranged for engagement with side surfaces of the projections ofsaid part, c. an additional roller element spaced from the first andprojecting from the annular portion of the support member and arrangedfor engagement with side surfaces of the projections of said part, d.anti-friction bearing devices carrying said roller elements insubstantially radial disposition with respect to said annular portion,and e. means for adjustably mounting said additional roller element onsaid member to enable adjustable positioning of the element axially ofsaid member whereby the position of the additional roller element can beadjustably shifted with respect to said first roller element to enableprecise and simultaneous engagement of both roller elements with therespective side surfaces of said shouldered part so as to enable saidmember to be used with shouldered parts made to non-critical tolerances.2. The invention as in claim 1, wherein: a. said support member hasmeans defining a socket radially disposed therein, and b. saidadjustable means comprising an eccentric bushing, the bore of which iseccentric with respect to the outer periphery, said bushing beingreceivable in said socket and turnable therein, c. said bushing carryingone of said anti-friction bearing devices and said additional rollerelement.
 3. The invention as in claim 2, and further including: a. meanscarried by said support member, for locking said bushing in differentadjusted positions in said socket.
 4. The invention as in claim 3,wherein: a. said annular portion has a tapped bore communicating withsaid socket, and b. said locking means comprises a set screw carried insaid bore and engageable with the exterior surface of said bushing. 5.The invention as in claim 3, wherein: a. said bushing has an externalannular shoulder, b. said socket having a corresponding annular shoulderadapted to abut against one surface of said bushing shoulder, c. saidsocket further having an annular recess adjacent to its shoulder, d. aspring washer adapted to abut against another surface of said bushingshoulder, and e. a split ring received in said recess and engaging thespring washer to thereby bias the bushing shoulder into engagement withthe socket shoulder and thus retain the bushing against removal from thesocket.
 6. The invention as in claim 3, wherein: a. said bushing has anexternal annular shoulder, b. said socket having a corresponding annularshoulder adapted to aBut against one surface of said bushing shoulder,c. said annular portion of the support member having a tapped borecommunicating with said socket, and d. said locking means comprising aset screw carried in said bore and engageable with the lateral surfaceof said bushing.
 7. The invention as in claim 3, wherein: a. saidbushing has keying means engageable by a tool for effecting rotationthereof, to facilitate adjustment of the position of said one rollerelement.
 8. The invention as in claim 2, wherein: a. said support memberhas means defining a second socket radially disposed therein, b. saidmounting means comprising an additional bushing adapted to be receivedin said second socket, c. said bushing carrying the other of saidanti-friction bearing devices and the first-mentioned roller element, d.said additional bushing and said first-mentioned roller element beingconcentric with one another.
 9. The invention as in claim 3, wherein: a.said bushing has an external annular shoulder, b. said socket having acorresponding annular shoulder adapted to abut against one surface ofsaid bushing shoulder c. said socket having an internally threadedportion, d. a screw having a hollow portion for receiving said eccentricbushing and having an annular end portion, e. said screw beingreceivable in said threaded portion, and f. the annular end portion ofthe screw engaging the annular shoulder of the bushing, whereby thelatter can be clamped between the socket shoulder and the end portion ofthe screw when the screw is tightened.
 10. The invention as in claim 9,wherein: a. said bushing has keying means engageable by a tool forturning it, and b. said screw having an access opening communicatingwith said hollow cup portion, so as to admit a tool to engage the keyingmeans to adjustably turn the bushing.
 11. The invention as in claim 3,wherein: a. said support member has a longitudinal bore to receive saidshouldered part, b. said bushing having an external annular shoulder, c.said socket having a corresponding annular shoulder adapted to abutagainst said bushing shoulder, d. said bushing being insertable in saidsocket from said longitudinal bore, and e. an annular centralizing ringdisposed within said bore for centralizing said shouldered part therein.12. The invention as in claim 1, wherein: a. said support member hasannular end portions, and b. a centralizing ring disposed at an endportion for centralizing the shouldered part in said member.
 13. Theinvention as in claim 2, wherein: a. said bushing has an inturned innerend to retain said one bearing device and said additional rollerelement.
 14. The invention as in claim 2, wherein: a. said bushingcarrying one of said anti-friction bearing devices and said additionalroller element constituting a unitary assemblage insertable in saidsocket as a unit, b. positioning means to limit the insertion of saidassemblage to a predetermined amount, and c. retainer means to holdcaptive the assemblage.
 15. The invention as in claim 14, and furtherincluding: a. means carried by said member for locking said assemblagein different adjusted positions.
 16. The invention as set forth in claim1, and further including: a. a shaft having a longitudinal groove,constituting said shouldered part, b. said roller elements engaging sidewalls of said groove, c. said side walls constituting the saidprojections of said shouldered part.
 17. The invention as set forth inclaim 16, wherein: a. said shaft has additional longitudinally extendinggrooves with side wall portions constituting other projections of saidshouldered part, and b. additional roller elements carried by saidsupport member, engaging the side walls of said additional grooves so asto more adequately carry the support member on the shaft.